A known stored-energy spring mechanism is disclosed in European patent application EP 0829892 A1. This application discloses a stored-energy spring which pressurizes a fluid located in a storage cylinder via a pressure body and a pressure piston, which is capable of moving in sliding fashion in the storage cylinder. This fluid causes a drive rod to move. The drive rod is fixed on a drive piston, which is capable of moving in sliding fashion in a working cylinder. If the working piston is moved with the working rod into a first end position, it can close the circuit breaker. If the working piston is moved with the working rod into a second end position, it can open the circuit breaker.
That region of the working cylinder in which the working rod is located can be hydraulically connected to the storage cylinder. There can be fluid there which is under a high pressure.
If that region of the working cylinder which is remote from the working rod is hydraulically connected to the storage cylinder, the fluid which is under a high pressure can be delivered to this region of the working cylinder and the working piston can be moved into the first end position.
If that region of the working cylinder which is remote from the working rod is hydraulically connected to a low pressure tank, the fluid can be delivered from this region of the working cylinder into the low-pressure tank and the working piston can be moved into the second end position.
With each switching cycle, for example, with a movement of the working piston into the first end position and back into the second end position, a certain amount of fluid therefore flows out of the storage cylinder into the low-pressure tank. This reduces the volume in the storage cylinder and the stored-energy spring pushes the pressure piston deeper into the storage cylinder. In the process, the stored-energy spring is extended further.
The stored-energy spring mechanism has a spring excursion switch, which identifies when the stored-energy spring has reached a maximum permissible extent. This is referred to below as the switch-on extent. The spring excursion switch then switches on a pump, which pumps fluid from the low-pressure tank into the storage cylinder, as a result of which the stored-energy spring is tensioned again and as a result of which its extent is reduced. The spring excursion switch identifies when the stored-energy spring has reached a predetermined extent. This is referred to below as the switch-off extent, and switches the pump off again.
The switch-off extent of the stored-energy spring is smaller than the switch-on extent. The extent of the stored-energy spring therefore follows a hysteresis. This is referred to below as recharging hysteresis.
The recharging hysteresis is controlled by the spring excursion switch. The spring excursion switch includes a linearly movable toothed rack, which is coupled to the stored-energy spring and drives a cam disk, via a gearwheel. The cam disk includes a first circumferential region with a comparatively small radius and a second circumferential region with a comparatively large radius. A flank region is located between the first circumferential region and the second circumferential region, with the extent of the cam disk in the radial direction increasing approximately linearly from the radius of the first circumferential region up to the radius of the second circumferential region within the flank region. The cam disk actuates a monostable pushbutton, which has switching hysteresis and has at least one switching contact.
When the stored-energy spring reaches the switch-on extent, the second circumferential region acts upon the pushbutton. The pushbutton is thus pushed until the switching contact closes, as a result of which the pump is switched on. While the stored-energy spring is now tensioned, the cam disk rotates and first the flank region and then the first circumferential region acts upon the pushbutton. Owing to the switching hysteresis of the pushbutton, the switching contact only opens when the first circumferential region acts upon the pushbutton and the pushbutton is almost completely relieved of load. As long as the flank region of the cam disk acts upon the pushbutton, the switching contact remains closed. If the first circumferential region of the cam shaft acts upon the pushbutton, the stored-energy spring has reached the switch-off extent and the switching contact opens, as a result of which the pump is switched off.
If the stored-energy spring extends during operation of the stored-energy spring mechanism, the cam disk rotates in the opposite direction and the pushbutton is acted upon first by the flank region and then by the second circumferential region. Owing to the switching hysteresis of the pushbutton, the switching contact only closes when the second circumferential region acts upon the pushbutton and the switch-on extent of the stored-energy spring has been reached. As long as the flank region of the cam disk is acting upon the pushbutton, the switching contact remains open.
The greater the recharging hysteresis, the more fluid can flow out of the storage cylinder into the low-pressure tank before the pump is switched on.